Speaking to the Treasury Select Committee, HMRC's chief executive, Lin Homer, said that some of these schemes required investors to pay into a potential litigation fighting fund and to promise not to come to any personal agreement or settlement with HMRC.

That, she said, should have set alarm bells ringing and was evidence of the true nature of these arrangements.

Debtors

In addition to being granted the powers to demand payment now for tax bills still in dispute, HMRC is also seeking additional powers to take money directly from individuals' bank accounts.

It says it needs this power in exceptional circumstances when tax bills that are not in dispute are still not paid.

It says there are some 17,000 of what Lin Homer called "recalcitrant debtors".

That proposal is currently undergoing a consultation process that ends in three weeks.

If approved by parliament, which is by no means certain, it will be in force in a year's time.